/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.MoreObjects;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.errorprone.annotations.DoNotCall;
import com.google.errorprone.annotations.concurrent.LazyInit;
import com.google.j2objc.annotations.RetainedWith;
import com.google.j2objc.annotations.Weak;

import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.Arrays;
import java.util.Collection;
import java.util.Comparator;
import java.util.Map;
import java.util.Map.Entry;
import javax.annotation.CheckForNull;

/**
 * A {@link SetMultimap} whose contents will never change, with many other important properties
 * detailed at {@link ImmutableCollection}.
 *
 * <p><b>Warning:</b> As in all {@link SetMultimap}s, do not modify either a key <i>or a value</i>
 * of a {@code ImmutableSetMultimap} in a way that affects its {@link Object#equals} behavior.
 * Undefined behavior and bugs will result.
 *
 * <p>See the Guava User Guide article on <a href=
 * "https://github.com/google/guava/wiki/ImmutableCollectionsExplained"> immutable collections</a>.
 *
 * @author Mike Ward
 * @since 2.0
 */
@GwtCompatible(serializable = true, emulated = true)
@ElementTypesAreNonnullByDefault
public class ImmutableSetMultimap<K, V> extends ImmutableMultimap<K, V>
        implements SetMultimap<K, V>
{

    /**
     * Returns the empty multimap.
     *
     * <p><b>Performance note:</b> the instance returned is a singleton.
     */
    // Casting is safe because the multimap will never hold any elements.
    @SuppressWarnings("unchecked")
    public static <K, V> ImmutableSetMultimap<K, V> of()
    {
        return (ImmutableSetMultimap<K, V>) EmptyImmutableSetMultimap.INSTANCE;
    }

    /**
     * Returns an immutable multimap containing a single entry.
     */
    public static <K, V> ImmutableSetMultimap<K, V> of(K k1, V v1)
    {
        ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
        builder.put(k1, v1);
        return builder.build();
    }

    /**
     * Returns an immutable multimap containing the given entries, in order. Repeated occurrences of
     * an entry (according to {@link Object#equals}) after the first are ignored.
     */
    public static <K, V> ImmutableSetMultimap<K, V> of(K k1, V v1, K k2, V v2)
    {
        ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
        builder.put(k1, v1);
        builder.put(k2, v2);
        return builder.build();
    }

    /**
     * Returns an immutable multimap containing the given entries, in order. Repeated occurrences of
     * an entry (according to {@link Object#equals}) after the first are ignored.
     */
    public static <K, V> ImmutableSetMultimap<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3)
    {
        ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
        builder.put(k1, v1);
        builder.put(k2, v2);
        builder.put(k3, v3);
        return builder.build();
    }

    /**
     * Returns an immutable multimap containing the given entries, in order. Repeated occurrences of
     * an entry (according to {@link Object#equals}) after the first are ignored.
     */
    public static <K, V> ImmutableSetMultimap<K, V> of(
            K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4)
    {
        ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
        builder.put(k1, v1);
        builder.put(k2, v2);
        builder.put(k3, v3);
        builder.put(k4, v4);
        return builder.build();
    }

    /**
     * Returns an immutable multimap containing the given entries, in order. Repeated occurrences of
     * an entry (according to {@link Object#equals}) after the first are ignored.
     */
    public static <K, V> ImmutableSetMultimap<K, V> of(
            K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5)
    {
        ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
        builder.put(k1, v1);
        builder.put(k2, v2);
        builder.put(k3, v3);
        builder.put(k4, v4);
        builder.put(k5, v5);
        return builder.build();
    }

    // looking for of() with > 5 entries? Use the builder instead.

    /**
     * Returns a new {@link Builder}.
     */
    public static <K, V> Builder<K, V> builder()
    {
        return new Builder<>();
    }

    /**
     * A builder for creating immutable {@code SetMultimap} instances, especially {@code public static
     * final} multimaps ("constant multimaps"). Example:
     *
     * <pre>{@code
     * static final Multimap<String, Integer> STRING_TO_INTEGER_MULTIMAP =
     *     new ImmutableSetMultimap.Builder<String, Integer>()
     *         .put("one", 1)
     *         .putAll("several", 1, 2, 3)
     *         .putAll("many", 1, 2, 3, 4, 5)
     *         .build();
     * }</pre>
     *
     * <p>Builder instances can be reused; it is safe to call {@link #build} multiple times to build
     * multiple multimaps in series. Each multimap contains the key-value mappings in the previously
     * created multimaps.
     *
     * @since 2.0
     */
    public static final class Builder<K, V> extends ImmutableMultimap.Builder<K, V>
    {
        /**
         * Creates a new builder. The returned builder is equivalent to the builder generated by {@link
         * ImmutableSetMultimap#builder}.
         */
        public Builder()
        {
            super();
        }

        @Override
        Collection<V> newMutableValueCollection()
        {
            return Platform.preservesInsertionOrderOnAddsSet();
        }

        /**
         * Adds a key-value mapping to the built multimap if it is not already present.
         */
        @CanIgnoreReturnValue
        @Override
        public Builder<K, V> put(K key, V value)
        {
            super.put(key, value);
            return this;
        }

        /**
         * Adds an entry to the built multimap if it is not already present.
         *
         * @since 11.0
         */
        @CanIgnoreReturnValue
        @Override
        public Builder<K, V> put(Entry<? extends K, ? extends V> entry)
        {
            super.put(entry);
            return this;
        }

        /**
         * {@inheritDoc}
         *
         * @since 19.0
         */
        @CanIgnoreReturnValue
        @Beta
        @Override
        public Builder<K, V> putAll(Iterable<? extends Entry<? extends K, ? extends V>> entries)
        {
            super.putAll(entries);
            return this;
        }

        @CanIgnoreReturnValue
        @Override
        public Builder<K, V> putAll(K key, Iterable<? extends V> values)
        {
            super.putAll(key, values);
            return this;
        }

        @CanIgnoreReturnValue
        @Override
        public Builder<K, V> putAll(K key, V... values)
        {
            return putAll(key, Arrays.asList(values));
        }

        @CanIgnoreReturnValue
        @Override
        public Builder<K, V> putAll(Multimap<? extends K, ? extends V> multimap)
        {
            for (Entry<? extends K, ? extends Collection<? extends V>> entry :
                    multimap.asMap().entrySet())
            {
                putAll(entry.getKey(), entry.getValue());
            }
            return this;
        }

        @CanIgnoreReturnValue
        @Override
        Builder<K, V> combine(ImmutableMultimap.Builder<K, V> other)
        {
            super.combine(other);
            return this;
        }

        /**
         * {@inheritDoc}
         *
         * @since 8.0
         */
        @CanIgnoreReturnValue
        @Override
        public Builder<K, V> orderKeysBy(Comparator<? super K> keyComparator)
        {
            super.orderKeysBy(keyComparator);
            return this;
        }

        /**
         * Specifies the ordering of the generated multimap's values for each key.
         *
         * <p>If this method is called, the sets returned by the {@code get()} method of the generated
         * multimap and its {@link Multimap#asMap()} view are {@link ImmutableSortedSet} instances.
         * However, serialization does not preserve that property, though it does maintain the key and
         * value ordering.
         *
         * @since 8.0
         */
        // TODO: Make serialization behavior consistent.
        @CanIgnoreReturnValue
        @Override
        public Builder<K, V> orderValuesBy(Comparator<? super V> valueComparator)
        {
            super.orderValuesBy(valueComparator);
            return this;
        }

        /**
         * Returns a newly-created immutable set multimap.
         */
        @Override
        public ImmutableSetMultimap<K, V> build()
        {
            Collection<Map.Entry<K, Collection<V>>> mapEntries = builderMap.entrySet();
            if (keyComparator != null)
            {
                mapEntries = Ordering.from(keyComparator).<K>onKeys().immutableSortedCopy(mapEntries);
            }
            return fromMapEntries(mapEntries, valueComparator);
        }
    }

    /**
     * Returns an immutable set multimap containing the same mappings as {@code multimap}. The
     * generated multimap's key and value orderings correspond to the iteration ordering of the {@code
     * multimap.asMap()} view. Repeated occurrences of an entry in the multimap after the first are
     * ignored.
     *
     * <p>Despite the method name, this method attempts to avoid actually copying the data when it is
     * safe to do so. The exact circumstances under which a copy will or will not be performed are
     * undocumented and subject to change.
     *
     * @throws NullPointerException if any key or value in {@code multimap} is null
     */
    public static <K, V> ImmutableSetMultimap<K, V> copyOf(
            Multimap<? extends K, ? extends V> multimap)
    {
        return copyOf(multimap, null);
    }

    private static <K, V> ImmutableSetMultimap<K, V> copyOf(
            Multimap<? extends K, ? extends V> multimap,
            @CheckForNull Comparator<? super V> valueComparator)
    {
        checkNotNull(multimap); // eager for GWT
        if (multimap.isEmpty() && valueComparator == null)
        {
            return of();
        }

        if (multimap instanceof ImmutableSetMultimap)
        {
            @SuppressWarnings("unchecked") // safe since multimap is not writable
            ImmutableSetMultimap<K, V> kvMultimap = (ImmutableSetMultimap<K, V>) multimap;
            if (!kvMultimap.isPartialView())
            {
                return kvMultimap;
            }
        }

        return fromMapEntries(multimap.asMap().entrySet(), valueComparator);
    }

    /**
     * Returns an immutable multimap containing the specified entries. The returned multimap iterates
     * over keys in the order they were first encountered in the input, and the values for each key
     * are iterated in the order they were encountered. If two values for the same key are {@linkplain
     * Object#equals equal}, the first value encountered is used.
     *
     * @throws NullPointerException if any key, value, or entry is null
     * @since 19.0
     */
    @Beta
    public static <K, V> ImmutableSetMultimap<K, V> copyOf(
            Iterable<? extends Entry<? extends K, ? extends V>> entries)
    {
        return new Builder<K, V>().putAll(entries).build();
    }

    /**
     * Creates an ImmutableSetMultimap from an asMap.entrySet.
     */
    static <K, V> ImmutableSetMultimap<K, V> fromMapEntries(
            Collection<? extends Map.Entry<? extends K, ? extends Collection<? extends V>>> mapEntries,
            @CheckForNull Comparator<? super V> valueComparator)
    {
        if (mapEntries.isEmpty())
        {
            return of();
        }
        ImmutableMap.Builder<K, ImmutableSet<V>> builder =
                new ImmutableMap.Builder<>(mapEntries.size());
        int size = 0;

        for (Entry<? extends K, ? extends Collection<? extends V>> entry : mapEntries)
        {
            K key = entry.getKey();
            Collection<? extends V> values = entry.getValue();
            ImmutableSet<V> set = valueSet(valueComparator, values);
            if (!set.isEmpty())
            {
                builder.put(key, set);
                size += set.size();
            }
        }

        return new ImmutableSetMultimap<>(builder.build(), size, valueComparator);
    }

    /**
     * Returned by get() when a missing key is provided. Also holds the comparator, if any, used for
     * values.
     */
    private final transient ImmutableSet<V> emptySet;

    ImmutableSetMultimap(
            ImmutableMap<K, ImmutableSet<V>> map,
            int size,
            @CheckForNull Comparator<? super V> valueComparator)
    {
        super(map, size);
        this.emptySet = emptySet(valueComparator);
    }

    // views

    /**
     * Returns an immutable set of the values for the given key. If no mappings in the multimap have
     * the provided key, an empty immutable set is returned. The values are in the same order as the
     * parameters used to build this multimap.
     */
    @Override
    public ImmutableSet<V> get(K key)
    {
        // This cast is safe as its type is known in constructor.
        ImmutableSet<V> set = (ImmutableSet<V>) map.get(key);
        return MoreObjects.firstNonNull(set, emptySet);
    }

    @LazyInit
    @RetainedWith
    @CheckForNull
    private transient ImmutableSetMultimap<V, K> inverse;

    /**
     * {@inheritDoc}
     *
     * <p>Because an inverse of a set multimap cannot contain multiple pairs with the same key and
     * value, this method returns an {@code ImmutableSetMultimap} rather than the {@code
     * ImmutableMultimap} specified in the {@code ImmutableMultimap} class.
     */
    @Override
    public ImmutableSetMultimap<V, K> inverse()
    {
        ImmutableSetMultimap<V, K> result = inverse;
        return (result == null) ? (inverse = invert()) : result;
    }

    private ImmutableSetMultimap<V, K> invert()
    {
        Builder<V, K> builder = builder();
        for (Entry<K, V> entry : entries())
        {
            builder.put(entry.getValue(), entry.getKey());
        }
        ImmutableSetMultimap<V, K> invertedMultimap = builder.build();
        invertedMultimap.inverse = this;
        return invertedMultimap;
    }

    /**
     * Guaranteed to throw an exception and leave the multimap unmodified.
     *
     * @throws UnsupportedOperationException always
     * @deprecated Unsupported operation.
     */
    @CanIgnoreReturnValue
    @Deprecated
    @Override
    @DoNotCall("Always throws UnsupportedOperationException")
    public final ImmutableSet<V> removeAll(@CheckForNull Object key)
    {
        throw new UnsupportedOperationException();
    }

    /**
     * Guaranteed to throw an exception and leave the multimap unmodified.
     *
     * @throws UnsupportedOperationException always
     * @deprecated Unsupported operation.
     */
    @CanIgnoreReturnValue
    @Deprecated
    @Override
    @DoNotCall("Always throws UnsupportedOperationException")
    public final ImmutableSet<V> replaceValues(K key, Iterable<? extends V> values)
    {
        throw new UnsupportedOperationException();
    }

    @LazyInit
    @RetainedWith
    @CheckForNull
    private transient ImmutableSet<Entry<K, V>> entries;

    /**
     * Returns an immutable collection of all key-value pairs in the multimap. Its iterator traverses
     * the values for the first key, the values for the second key, and so on.
     */
    @Override
    public ImmutableSet<Entry<K, V>> entries()
    {
        ImmutableSet<Entry<K, V>> result = entries;
        return result == null ? (entries = new EntrySet<>(this)) : result;
    }

    private static final class EntrySet<K, V> extends ImmutableSet<Entry<K, V>>
    {
        @Weak
        private final transient ImmutableSetMultimap<K, V> multimap;

        EntrySet(ImmutableSetMultimap<K, V> multimap)
        {
            this.multimap = multimap;
        }

        @Override
        public boolean contains(@CheckForNull Object object)
        {
            if (object instanceof Entry)
            {
                Entry<?, ?> entry = (Entry<?, ?>) object;
                return multimap.containsEntry(entry.getKey(), entry.getValue());
            }
            return false;
        }

        @Override
        public int size()
        {
            return multimap.size();
        }

        @Override
        public UnmodifiableIterator<Entry<K, V>> iterator()
        {
            return multimap.entryIterator();
        }

        @Override
        boolean isPartialView()
        {
            return false;
        }
    }

    private static <V> ImmutableSet<V> valueSet(
            @CheckForNull Comparator<? super V> valueComparator, Collection<? extends V> values)
    {
        return (valueComparator == null)
                ? ImmutableSet.copyOf(values)
                : ImmutableSortedSet.copyOf(valueComparator, values);
    }

    private static <V> ImmutableSet<V> emptySet(@CheckForNull Comparator<? super V> valueComparator)
    {
        return (valueComparator == null)
                ? ImmutableSet.<V>of()
                : ImmutableSortedSet.<V>emptySet(valueComparator);
    }

    private static <V> ImmutableSet.Builder<V> valuesBuilder(
            @CheckForNull Comparator<? super V> valueComparator)
    {
        return (valueComparator == null)
                ? new ImmutableSet.Builder<V>()
                : new ImmutableSortedSet.Builder<V>(valueComparator);
    }

    /**
     * @serialData number of distinct keys, and then for each distinct key: the key, the number of
     * values for that key, and the key's values
     */
    @GwtIncompatible // java.io.ObjectOutputStream
    private void writeObject(ObjectOutputStream stream) throws IOException
    {
        stream.defaultWriteObject();
        stream.writeObject(valueComparator());
        Serialization.writeMultimap(this, stream);
    }

    @CheckForNull
    Comparator<? super V> valueComparator()
    {
        return emptySet instanceof ImmutableSortedSet
                ? ((ImmutableSortedSet<V>) emptySet).comparator()
                : null;
    }

    @GwtIncompatible // java serialization
    private static final class SetFieldSettersHolder
    {
        static final Serialization.FieldSetter<ImmutableSetMultimap> EMPTY_SET_FIELD_SETTER =
                Serialization.getFieldSetter(ImmutableSetMultimap.class, "emptySet");
    }

    @GwtIncompatible // java.io.ObjectInputStream
    // Serialization type safety is at the caller's mercy.
    @SuppressWarnings("unchecked")
    private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException
    {
        stream.defaultReadObject();
        Comparator<Object> valueComparator = (Comparator<Object>) stream.readObject();
        int keyCount = stream.readInt();
        if (keyCount < 0)
        {
            throw new InvalidObjectException("Invalid key count " + keyCount);
        }
        ImmutableMap.Builder<Object, ImmutableSet<Object>> builder = ImmutableMap.builder();
        int tmpSize = 0;

        for (int i = 0; i < keyCount; i++)
        {
            Object key = stream.readObject();
            int valueCount = stream.readInt();
            if (valueCount <= 0)
            {
                throw new InvalidObjectException("Invalid value count " + valueCount);
            }

            ImmutableSet.Builder<Object> valuesBuilder = valuesBuilder(valueComparator);
            for (int j = 0; j < valueCount; j++)
            {
                valuesBuilder.add(stream.readObject());
            }
            ImmutableSet<Object> valueSet = valuesBuilder.build();
            if (valueSet.size() != valueCount)
            {
                throw new InvalidObjectException("Duplicate key-value pairs exist for key " + key);
            }
            builder.put(key, valueSet);
            tmpSize += valueCount;
        }

        ImmutableMap<Object, ImmutableSet<Object>> tmpMap;
        try
        {
            tmpMap = builder.build();
        }
        catch (IllegalArgumentException e)
        {
            throw (InvalidObjectException) new InvalidObjectException(e.getMessage()).initCause(e);
        }

        FieldSettersHolder.MAP_FIELD_SETTER.set(this, tmpMap);
        FieldSettersHolder.SIZE_FIELD_SETTER.set(this, tmpSize);
        SetFieldSettersHolder.EMPTY_SET_FIELD_SETTER.set(this, emptySet(valueComparator));
    }

    @GwtIncompatible // not needed in emulated source.
    private static final long serialVersionUID = 0;
}
